1. Field of the Invention
The present invention relates to a driving system for a four-wheel drive working vehicle comprising a hydrostatic transmission (an HST) for driving main-driving wheels, a hydraulic pump, and one or more hydraulic motors for driving sub-driving wheels, wherein output power from the hydraulic motor of the HST for the main-driving wheels is partly transmitted to the hydraulic pump for the sub-driving wheels through another transmission. The present invention also relates to a construction for decelerating the main-driving wheels, wherein a working machine is provided in front of a vehicle body.
2. Related Art
Japanese Utility Model Laid-Open No. Sho 60-32127, for example, discloses a conventional four-wheel drive vehicle provided with an HST. An engine drives a hydraulic motor through a hydraulic pump fluidly connected with the hydraulic motor. The hydraulic motor transmits power to a differential gear unit through a mechanical sub-transmission for the purpose of driving main-driving wheels (rear wheels or front wheels). The hydraulic motor also partly transmits power to another differential gear unit through a transmitting shaft for the purpose of driving sub-driving wheels (front wheels or rear wheels).
Also, Japanese Laid-Open No. Hei 9-121645, for example, discloses a conventional working vehicle having a working machine such as a mower provided either in front of the vehicle body or at its venter portion between its front wheels and rear wheels.
In this conventional construction, the rotary speed of the sub-driving wheels is different from that ofthe main-driving wheels because the main-driving wheels receive the transmitted power through the sub-transmission. Thus, a problem exists whereby the faster wheels, which are either the main-driving wheels or the sub-driving wheels (the front wheels or the rear wheels), drag the other wheels and a working machine provided on the vehicle. This can cause significant injury to the ground surface (e.g., of a farm), especially if the working vehicle is provided with a mower.
Even if the rotary speeds of the main-driving wheels and the sub-driving wheels (front and rear wheels) are equalized, the four-wheel drive working vehicle turns around an inside main-driving wheel. Therefore, the rotary speed of both sub-driving wheels, which are rather apart from the inside main-driving wheel, slows down so as to be dragged. When the working vehicle travels in two-wheel drive, where only the main-driving wheels are driven, if one of either the left or the right main-driving wheels runs idle, the other main-driving wheel slips because it cannot receive the driving power. This also can cause injury to the ground surface.
For the latter construction, a plurality of mowers are occasionally juxtaposed on a lateral row (arranged on in the center, one on the left and one on the right, for example), so that they can cut the grass in a wide lateral range. In this case, the mowers overlap one another when viewed from the front, so as to leave no uncut grass.
Consequently, these mowers do not overlap when viewed from the side. This causes the size of the working vehicle to increase longitudinally. Furthermore, a center mower of the arrangement must be vertically and movably suspended by a long arm. Accordingly, it is necessary to reinforce the strength of the arm and the lifting power thereof, especially when the center mower is disposed at the fore-end of the vehicle body (before left and right mowers). Additionally, for preventing the vehicle with the mowers from turning along a large turning radius, the overlapping portions of the center mower with the left and right mowers are necessarily lengthened, thereby causing much unevenness of the cut between the portion where the mowers overlap and the portion where they do not overlap.
Where the mower is disposed at the venter portion of the working vehicle between the front wheels and the rear wheels, a transmitting shaft is necessarily interposed between the output shaft of the hydraulic motor and the differential gear unit of the sub-driving wheels (front wheels or rear wheels), thereby restricting the space for disposal of the mower.